Try It Yourself - SyntaxStudy Editor

HTML / CSS / JS

import kotlinx.coroutines.*
import kotlin.system.measureTimeMillis

suspend fun fetchUser(id: Int): String {
    delay(500)   // simulate network call
    return "User#$id"
}

suspend fun fetchScore(userId: String): Int {
    delay(300)   // simulate DB query
    return userId.length * 10
}

fun main() = runBlocking {
    // Sequential — ~800 ms
    val seqMs = measureTimeMillis {
        val user  = fetchUser(1)
        val score = fetchScore(user)
        println("Sequential: $user -> $score")
    }
    println("Sequential took: ${seqMs}ms")

// Parallel with async/await — ~500 ms
    val parMs = measureTimeMillis {
        val deferredUser  = async { fetchUser(1) }
        val deferredUser2 = async { fetchUser(2) }

val user1 = deferredUser.await()
        val user2 = deferredUser2.await()
        println("Parallel: $user1 and $user2")
    }
    println("Parallel took: ${parMs}ms")

// awaitAll on a list
    val users = (1..5).map { id -> async { fetchUser(id) } }.awaitAll()
    println("All users: $users")

// async with explicit start (lazy)
    val lazy = async(start = CoroutineStart.LAZY) { fetchUser(99) }
    println("Lazy not started yet")
    println(lazy.await())   // starts here
}